A high-frequency compatible low-loss leaky coaxial cable and a method for manufacturing the same

Abstract

This invention discloses a high-frequency compatible low-loss leaky coaxial cable and its manufacturing method, comprising, from the inside out, an inner conductor, a composite insulation layer, a radiating outer conductor, an absorbing layer, and a composite sheath layer. The invention employs a hollow corrugated inner conductor and a high-foaming polytetrafluoroethylene (PTFE) layer to effectively suppress skin effect loss and dielectric loss in the 10-100 GHz frequency band. It utilizes a single rectangular slot structure with exponentially increasing axial period length, abandoning the complex scheme of traditional multi-slot designs for different frequency bands, thus progressively enhancing radiated energy from low to high frequencies and avoiding mode abrupt changes and radiation discontinuities between different frequency bands, achieving a VSWR < 1.2 within the 1-100 GHz wideband. The absorbing layer effectively absorbs surface waves and higher-order modes above 30 GHz, preventing signal distortion. Nanonucleating agents and perfluoroalkyl ether crystallization modifiers are introduced into the PTFE foaming system, combined with femtosecond laser grooving technology, to achieve micron-level foam cells and burr-free slots.

Description

Technical Field

[0001] This invention belongs to the field of leaky coaxial cable technology, specifically relating to a high-frequency compatible low-loss leaky coaxial cable and its preparation method. Background Technology

[0002] With the large-scale commercialization of 5G networks, the industry has begun research on sixth-generation mobile communication technology (6G). 6G networks will expand into millimeter wave and terahertz frequency bands to achieve ultra-high bandwidth (peak rate >1Tbps) and sub-millisecond latency. However, high-frequency signals suffer from extremely high path loss when transmitted in free space and traditional media, resulting in a sharp reduction in coverage distance.

[0003] Leaky coaxial cables are widely used in existing 4G / 5G networks as a key transmission medium for special scenarios such as indoor coverage, tunnels, and rail transit. However, traditional leaky cables face the following technical bottlenecks when evolving to 6G high frequencies: 1) High-frequency attenuation: Existing leaky cables using physically foamed polyethylene (PE) or polyolefin as insulation medium experience a sharp increase in dielectric loss tangent (>0.0005) at high frequencies (>10GHz). At the same time, the skin effect causes conductor loss to increase in multiples of the square root of the frequency, resulting in extremely short signal transmission distances. At 100GHz, the attenuation constant is usually greater than 10dB / 100m, which cannot meet the 6G coverage requirements. 2) Conflict between radiation efficiency and transmission loss: To support high-frequency coverage, a denser or more open slot structure is required, but this will exacerbate the longitudinal transmission loss of the cable, causing the signal energy to be radiated out too early, making it impossible to achieve long-distance coverage. 3) Mode dispersion and higher-order mode interference: When operating in ultra-wideband (e.g., covering 0.6GHz-100GHz), higher-order mode transmission modes will be excited inside the leaky cable, resulting in signal distortion and radiation pattern disorder, which seriously affects the high fidelity requirements of 6G communication.

[0004] In addition, most existing leaky cables use a single slot design with periodic arrangement along the axial direction (such as figure-eight slot, U-shaped slot or E-shaped slot), which makes it difficult to balance high-frequency radiation efficiency and low-frequency transmission performance. Summary of the Invention

[0005] To address the problems in the prior art, the present invention aims to provide a high-frequency compatible low-loss leakage coaxial cable and its preparation method.

[0006] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows: A high-frequency compatible low-loss leaky coaxial cable comprises, from the inside out, an inner conductor, a composite insulation layer, a radiating outer conductor, a wave-absorbing layer, and a composite sheath layer.

[0007] Furthermore, the inner conductor is a hollow corrugated copper tube structure, filled with a gas or a cross-shaped support frame with a dielectric constant close to 1.

[0008] Furthermore, the composite insulation layer comprises a polytetrafluoroethylene (PTFE) layer with a foaming degree of 85-92% and an ultra-thin, dense surface layer covering the PTFE layer. The PTFE layer has a pore diameter of less than 100 μm and a pore density of greater than 10. 9 pcs / cm 3 .

[0009] Furthermore, the formulation of the polytetrafluoroethylene layer includes, by weight, 100 parts of PTFE dispersion resin, 3-8 parts of nano-nucleating agent, 0.2-0.5 parts of hindered phenolic antioxidant, 0.5-1 parts of perfluoroalkyl ether crystallization regulator, and supercritical nitrogen gas accounting for 1.5-3.5% of the total resin mass as a foaming agent.

[0010] Furthermore, the outer radiating conductor is provided with an array of rectangular slots arranged periodically along the axial direction. The long side of the rectangular slots makes an angle of 10°-20° with the cable axis. Adjacent rows of rectangular slots are staggered in the axial direction, with a staggering distance of 1 / 4-1 / 2 of the length of the rectangular slots. The two ends of the rectangular slots are provided with semi-circular chamfers with a radius of 0.2-0.5mm.

[0011] Furthermore, the periodic length of the rectangular slot increases exponentially along the axial direction, and the width of the rectangular slot is 0.3-1.2 mm and the length is 2-8 mm.

[0012] Furthermore, the formulation of the microwave absorbing layer includes, by weight, 100 parts of polymer substrate, 40-60 parts of carbonyl iron powder, 20-30 parts of hexagonal ferrite, 1-5 parts of carbon nanotubes, 1-3 parts of coupling agent, and 2-5 parts of dispersant.

[0013] Furthermore, the thickness of the absorbing layer is 0.2-0.5 mm.

[0014] Furthermore, the outer radiating conductor is a longitudinally welded annular corrugated copper tube; the composite sheath layer includes a flame-retardant polyolefin inner layer and an ultraviolet-resistant, low-friction sheath outer layer extruded onto its exterior.

[0015] This invention also discloses a method for preparing a high-frequency compatible low-loss leakage coaxial cable, comprising the following steps: S1: The copper strip is rolled into a round tube, the longitudinal seam is welded, and the diameter is expanded by rotation to form a hollow corrugated copper tube structure, forming an inner conductor, which is filled with gas or a support skeleton with a dielectric constant close to 1. S2: Mix 100 parts of PTFE dispersion resin, 3-8 parts of nano nucleating agent, 0.2-0.5 parts of hindered phenolic antioxidant and 0.5-1 parts of perfluoroalkyl ether crystallization regulator evenly, and inject 1.5-3.5% of supercritical nitrogen gas as a foaming agent. Extrude the mixture onto the inner conductor at 20-35 MPa and 350-380℃ to form a microporous polytetrafluoroethylene layer. Then, co-extrude cross-linked polyethylene onto the outside of the microporous polytetrafluoroethylene layer to form an ultra-thin and dense surface layer, and finally obtain a composite insulation layer. S3: Copper strip is wrapped on the composite insulation layer, longitudinally welded to form a copper tube, and then annular corrugation is performed; S4: Use femtosecond laser cutting technology to open a rectangular slot array on the outer conductor obtained in step S3, control the axial misalignment distance between two adjacent rows of rectangular slots, the pulse width of femtosecond laser cutting is less than 500 femtoseconds, and the repetition frequency is 100kHz-1MHz; S5: The microwave absorbing band is prepared by using 100 parts of polymer substrate, 40-60 parts of carbonyl iron powder, 20-30 parts of hexagonal ferrite, 1-5 parts of carbon nanotubes, 1-3 parts of coupling agent and 2-5 parts of dispersant. It is then longitudinally wrapped or wrapped around the grooved outer radiation conductor, and finally a double-layer co-extruded composite sheath layer is formed.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) High frequency and low loss: The hollow corrugated inner conductor + high foaming polytetrafluoroethylene layer (equivalent dielectric constant is reduced to 1.25-1.35) effectively suppresses skin effect loss and dielectric loss in the 10GHz-100GHz frequency band. The transmission distance of 6G high frequency signal is increased by more than 50% compared with traditional PE foamed leaky cable. (2) Uniform radiation performance over a wide frequency band: The single rectangular slot structure with an exponentially increasing period length along the axial direction is adopted, which abandons the complex scheme of the traditional multi-slot design for frequency bands. This makes the radiation energy gradually enhanced from low frequency to high frequency, avoiding mode abrupt changes and radiation discontinuity between different frequency bands. VSWR<1.2 in the 1-100GHz wide frequency band. (3) High-order mode suppression: The unique magnetic / dielectric absorbing layer (carbonyl iron powder + hexagonal ferrite + carbon nanotube) effectively absorbs surface waves and high-order modes above 30GHz, avoiding signal distortion; (4) Synergistic innovation of formulation and process: Nano nucleating agent and perfluoroalkyl ether crystallization regulator are introduced into PTFE foaming system and combined with femtosecond laser grooving process to achieve micron-level foam pores and burr-free grooves. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a planar structural diagram of the rectangular slot array of the present invention; Figure 3 The curves show the attenuation constants of Embodiment 1 of the present invention and existing leaky cables in the 1-100GHz frequency band. Figure 4 The reflection loss curve of the absorbing layer in Embodiment 1 of the present invention in the 30-100GHz frequency band is shown. Figure 5 This is a schematic diagram showing the exponential increase in the axial periodic length of the rectangular slot hole of the present invention. Among them, 1-inner conductor, 2-composite insulation layer, 21-polytetrafluoroethylene layer, 22-ultra-thin dense surface layer, 3-radiative outer conductor, 4-wave absorbing layer, 5-composite sheath layer, 51-flame retardant polyolefin inner layer, 52-UV resistant low-friction sheath outer layer. Detailed Implementation

[0018] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0019] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0020] like Figure 1-5 As shown, this invention discloses a high-frequency compatible low-loss leaky coaxial cable for 6G communication. From the inside out, it includes an inner conductor 1, a composite insulation layer 2, a radiating outer conductor 3, and a composite sheath layer 5. An absorbing layer 4 is provided between the radiating outer conductor 3 and the composite sheath layer 5 to absorb surface waves and higher-order modes above 30GHz. It has stable transmission and radiation performance in the 1GHz-100GHz wideband, ensuring the coverage quality of 6G communication in indoor and tunnel scenarios.

[0021] The inner conductor 1 is a hollow corrugated copper tube structure, filled with a gas (such as dry nitrogen) with a dielectric constant close to 1 or a cross-shaped support frame, which is used to reduce the skin effect conductor loss at high frequencies. The hollow structure makes the high-frequency current mainly distributed on the outer surface of the copper tube, and the equivalent conductor loss is significantly reduced.

[0022] The composite insulation layer 2 includes a microporous polytetrafluoroethylene (PTFE) layer 21 with a foaming degree of 85-92%. The PTFE layer 21 has a pore diameter of less than 100 μm and a pore density of greater than 10. 9 pcs / cm 3The PTFE substrate itself has an extremely low dielectric loss tangent (<0.0002@100GHz), and with its ultra-high foaming degree, the equivalent dielectric constant can be reduced to 1.25-1.35.

[0023] The composite insulation layer 2 also includes an ultra-thin dense surface layer 22 that is coated on the polytetrafluoroethylene layer 21 by a co-extrusion process. The ultra-thin dense surface layer 22 is made of low-loss cross-linked polyethylene with a thickness of 0.1-0.2 mm. It is used to isolate the polytetrafluoroethylene layer from the radiating outer conductor, prevent high-frequency electric field distortion, and improve the adhesion between the composite insulation layer 2 and the radiating outer conductor 3.

[0024] In some embodiments, the formulation of the polytetrafluoroethylene layer 21 includes, by weight, 100 parts of PTFE dispersion resin, 3-8 parts of nano-nucleating agent (polyimide PI nanopowder or boron nitride BN nanopowder, particle size 50-200nm), 0.2-0.5 parts of hindered phenolic antioxidant (Irganox 1010), 0.5-1 parts of perfluoroalkyl ether crystallization regulator, and injects 1.5-3.5% of supercritical nitrogen gas as a foaming agent, with an injection pressure of 20-35MPa and a temperature of 350-380℃.

[0025] The synergistic effect of perfluoroalkyl ether crystallization regulator and nano nucleating agent is as follows: the nano nucleating agent provides a large number of uniform nucleation sites, and the perfluoroalkyl ether regulates the crystallization rate of PTFE and prevents the pores from merging and growing, thereby obtaining a closed-cell structure with a pore size of less than 100 μm and a uniform pore size distribution.

[0026] The surface of the radiating outer conductor 3 is periodically opened with an array of rectangular slots arranged at unequal intervals along the axial direction. The long side of the rectangular slots makes an angle of 10°-20° with the cable axial direction. Adjacent rows of rectangular slots are staggered in the axial direction, with a staggering distance of 1 / 4-1 / 2 of the length of the rectangular slot. The two ends of the rectangular slots are provided with semi-circular chamfers with a radius of 0.2-0.5mm.

[0027] In some embodiments, the outer radiating conductor 3 is a longitudinally welded annular corrugated copper tube.

[0028] In some implementations, the period length of the rectangular slot increases exponentially along the axial direction.

[0029] In some implementations, the width of the rectangular slot is 0.3-1.2 mm and the length is 2-8 mm.

[0030] In some implementations, the rectangular slot is formed by femtosecond laser cutting, with a burr height of less than 5 μm.

[0031] The key difference between the slot structure of this invention and the prior art is that it adopts a single rectangular slot with an exponentially increasing period length along the axial direction. This eliminates the complex scheme of opening different slot types for high-frequency and low-frequency bands in traditional leaky cables. By exponentially changing the period length, it achieves progressive radiation enhancement from low frequency to high frequency, avoiding the mode change problem that may be caused by frequency segmentation design.

[0032] In some embodiments, the formulation of the microwave absorbing layer 4 comprises, by weight, 100 parts of a polymer substrate (polypropylene PP or thermoplastic polyurethane TPU), 40-60 parts of carbonyl iron powder (CIP, particle size 1-5 μm), and hexagonal ferrite (BaFe). 12 O 19 or SrFe 12 O 19 20-30 parts of particle size 0.5-2μm, 1-5 parts of carbon nanotubes (CNT), 1-3 parts of coupling agent (titanium ester or silane KH-550), and 2-5 parts of dispersant (polyethylene wax).

[0033] The carbonyl iron powder + hexagonal ferrite + carbon nanotube ternary composite system: carbonyl iron powder provides magnetic loss, hexagonal ferrite provides high-frequency dielectric loss, and carbon nanotubes form a conductive network to enhance multiple reflection absorption. The synergy of the three makes the reflection loss of the absorbing layer >10dB in the 30-100GHz range.

[0034] The innovative aspect of the absorbing layer 4 formulation of this invention, which differs from existing technologies, lies in the following: While binary composites of carbonyl iron powder and carbon nanotubes have been reported in the literature, the key to this invention is the introduction of hexagonal ferrite as a third component. Its unique hexagonal crystal structure possesses natural resonant absorption characteristics in the millimeter-wave band, which can complement the eddy current loss of carbonyl iron powder, thereby achieving broad-spectrum coverage across the entire 30-100 GHz frequency band. Existing technologies mainly focus on low-frequency absorbing applications in the 2-18 GHz range, lacking systematic research on high-frequency absorbing above 30 GHz.

[0035] In some embodiments, the thickness of the absorbing layer 4 is 0.2-0.5 mm.

[0036] In some embodiments, the composite sheath layer 5 includes a flame-retardant polyolefin inner layer 51 and an ultraviolet-resistant, low-friction sheath outer layer 52 extruded onto the outside of it.

[0037] This invention also discloses a method for preparing the high-frequency compatible low-loss leakage coaxial cable as described above, comprising the following steps: S1: The copper strip is rolled into a round tube, the longitudinal seam is welded, and the diameter is expanded by rotation to form a hollow corrugated copper tube structure, forming the inner conductor 1, which is filled with gas or a support skeleton with a dielectric constant close to 1. S2: Mix 100 parts of PTFE dispersion resin, 3-8 parts of nano nucleating agent, 0.2-0.5 parts of hindered phenolic antioxidant and 0.5-1 parts of perfluoroalkyl ether crystallization regulator evenly, and inject 1.5-3.5% of supercritical nitrogen gas as a foaming agent. Extrude the mixture onto the inner conductor 1 at 20-35 MPa and 350-380℃ to form a polytetrafluoroethylene layer 21. Then, co-extrude cross-linked polyethylene onto the polytetrafluoroethylene layer 21 to form an ultra-thin and dense surface layer 22, and finally obtain the composite insulation layer 2. S3: Copper strip is wrapped around composite insulation layer 2, longitudinally welded to form copper tube, and then annular embossing is performed; S4: Use femtosecond laser cutting technology to open a rectangular slot array on the outer conductor obtained in step S3, control the axial misalignment distance between two adjacent rows of rectangular slots, the pulse width of femtosecond laser cutting is less than 500 femtoseconds, and the repetition frequency is 100kHz-1MHz; S5: An absorbing band is prepared by using 100 parts of polymer substrate, 40-60 parts of carbonyl iron powder, 20-30 parts of hexagonal ferrite, 1-5 parts of carbon nanotubes, 1-3 parts of coupling agent and 2-5 parts of dispersant. It is then longitudinally wrapped or wrapped around the grooved outer radiation conductor 3, and finally a double-layer co-extruded composite sheath layer 5 is formed.

[0038] The high-frequency compatible low-loss leaky coaxial cable provided by this invention achieves an attenuation constant of <5dB / 100m@100GHz and a VSWR of <1.2 in a wide frequency band of 1GHz-100GHz, and effectively suppresses high-order mode interference, significantly improving the transmission distance and coverage quality of 6G high-frequency signals, and is suitable for complex environments such as indoors and tunnels.

[0039] The performance specifications of the high-frequency compatible low-loss leakage coaxial cable provided by this invention are as follows: At 100GHz, the attenuation constant is <5dB / 100m; Within the 1-100 GHz range, the voltage standing wave ratio (VSWR) is <1.2; Dielectric loss tangent < 0.0008 (@100GHz); The absorbing layer 4 exhibits a reflection loss of >10dB and surface wave suppression of >15dB in the 30-100GHz range.

[0040] Example 1

[0041] like Figure 1-5 As shown, a high-frequency compatible low-loss leaky coaxial cable for 6G communication is provided. The cable has a specification of 1 / 2 inch and includes, from the inside out, an inner conductor 1, a composite insulation layer 2, a radiating outer conductor 3, and a composite sheath layer 5. An absorbing layer 4 is provided between the radiating outer conductor 3 and the composite sheath layer 5.

[0042] The inner conductor 1 is a hollow corrugated copper tube with an inner diameter of 5 mm and an outer diameter of 6.5 mm, and is filled with dry nitrogen gas.

[0043] The composite insulation layer 2 includes a microporous polytetrafluoroethylene (PTFE) layer 21 with a foaming degree of 88%, the PTFE layer 21 having a pore diameter of 80 μm and a pore density greater than 10. 9 pcs / cm 3 .

[0044] The formulation of polytetrafluoroethylene layer 21, by weight, includes: 100 parts of PTFE dispersion resin, 5 parts of nano-nucleating agent (boron nitride BN nanopowder, particle size 100nm), 0.3 parts of hindered phenolic antioxidant (Irganox 1010), 0.8 parts of perfluoroalkyl ether crystallization regulator, and injects supercritical nitrogen gas accounting for 2.5% of the total resin mass as a foaming agent at an injection pressure of 30MPa and a temperature of 370℃.

[0045] The composite insulation layer 2 also includes an ultra-thin dense surface layer 22 that is coated on the polytetrafluoroethylene layer 21 by a co-extrusion process. The ultra-thin dense surface layer 22 is made of low-loss cross-linked polyethylene with a thickness of 0.15 mm. It is used to isolate the polytetrafluoroethylene layer 21 from the radiating outer conductor 3, prevent high-frequency electric field distortion, and improve the adhesion between the composite insulation layer 2 and the radiating outer conductor 3.

[0046] The outer radiating conductor 3 is a longitudinally welded annular corrugated copper tube with a thickness of 0.2 mm. The surface of the outer radiating conductor 3 has a periodically arranged array of rectangular slots with unequal spacing along the axial direction. The long side of each rectangular slot forms a 15° angle with the cable axis. Adjacent rows of rectangular slots are staggered axially. The width of each rectangular slot is 0.5 mm, and its length is 4 mm. The ends of each rectangular slot have semi-circular chamfers with a radius of 0.3 mm. The staggered spacing between adjacent rows of slots is 1.5 mm, and the period length increases exponentially from 8 mm at the beginning to 25 mm at the end.

[0047] The rectangular slot is formed by femtosecond laser cutting, with a burr height of less than 5μm.

[0048] The formulation of the microwave absorbing layer 4, by weight, includes: 100 parts of polymer substrate (thermoplastic polyurethane TPU), 50 parts of carbonyl iron powder (CIP, particle size 3μm, flake form, ball-milled for 6 hours), and hexagonal ferrite (BaFe). 12 O 19 The mixture consists of 25 parts of a particle size of 0.5 μm, 3 parts of carbon nanotubes (CNTs), 2 parts of a coupling agent (silane KH-550), and 3 parts of a dispersant (polyethylene wax). The mixture is then calendered into a 0.3 mm thick strip and longitudinally wrapped around a radiating outer conductor.

[0049] The composite sheath layer 5 includes a flame-retardant polyolefin inner layer 51 (0.8 mm thick) and an ultraviolet-resistant, low-friction outer sheath layer 52 (0.4 mm thick) extruded onto the outside, which are formed by double-layer co-extrusion.

[0050] A method for manufacturing a high-frequency compatible, low-loss, leaky coaxial cable includes the following steps: S1: The copper strip is rolled into a round tube, the longitudinal seam is welded, and the diameter is expanded by rotation to form a hollow corrugated copper tube structure, forming the inner conductor 1 with an inner diameter of 5mm and an outer diameter of 6.5mm, and the interior is filled with dry nitrogen. S2: 100 parts of PTFE dispersion resin, 5 parts of nano-nucleating agent (boron nitride BN nanopowder, particle size 100nm), 0.3 parts of hindered phenolic antioxidant (Irganox 1010), and 0.8 parts of perfluoroalkyl ether crystallization regulator are mixed and injected with supercritical nitrogen gas accounting for 2.5% of the total resin mass as a foaming agent (injection pressure 30MPa, temperature 370℃). The mixture is extruded onto the inner conductor 1 at 20MPa and 350℃ to form a polytetrafluoroethylene layer 21. Then, cross-linked polyethylene is co-extruded over the polytetrafluoroethylene layer 21 to form an ultra-thin and dense surface layer 22, and finally, a composite insulation layer 2 is obtained. S3: Copper strip is wrapped around composite insulation layer 2, longitudinally welded to form copper tube, and then annular embossing is performed; S4: Use femtosecond laser cutting technology to open a rectangular slot array on the outer conductor obtained in step S3, control the axial misalignment distance between two adjacent rows of rectangular slots, the pulse width of the femtosecond laser cutting is 400 femtoseconds, and the repetition frequency is 500kHz. S5: Composed of 100 parts of polymer matrix (thermoplastic polyurethane TPU), 50 parts of carbonyl iron powder (CIP, particle size 3μm, flake form, ball-milled for 6 hours), and hexagonal ferrite (BaFe). 12 O 19 The mixture of 25 parts of 0.5μm particle size, 3 parts of carbon nanotubes (CNT), 2 parts of coupling agent (silane KH-550), and 3 parts of dispersant (polyethylene wax) is calendered into a 0.3mm thick strip, which is then longitudinally wrapped onto the grooved outer radiation conductor 3, and finally a double-layer co-extruded composite sheath layer 5.

[0051] The performance specifications of the high-frequency compatible low-loss leaky coaxial cable provided in this embodiment are as follows: At 100GHz, the attenuation constant is 4.3dB / 100m; The voltage standing wave ratio (VSWR) is 1.19 in the 1-100 GHz range; The absorbing layer 4 achieves a reflection loss of 12dB at 60GHz.

[0052] Example 2

[0053] like Figure 1As shown, a high-frequency compatible low-loss leaky coaxial cable for 6G communication includes, from the inside out, an inner conductor 1, a composite insulation layer 2, a radiating outer conductor 3, and a composite sheath layer 5, wherein an absorbing layer 4 is provided between the radiating outer conductor 3 and the composite sheath layer 5.

[0054] The inner conductor 1 is a hollow corrugated copper tube with an inner diameter of 6.5 mm and an outer diameter of 8.5 mm, and is filled with dry nitrogen gas.

[0055] The composite insulation layer 2 includes a microporous polytetrafluoroethylene (PTFE) layer 21 with a foaming degree of 90%, the PTFE layer 21 having a pore diameter of 65 μm and a pore density greater than 10. 9 pcs / cm 3 .

[0056] The formulation of polytetrafluoroethylene layer 21 includes, by weight, 100 parts of PTFE dispersion resin, 6 parts of nano-nucleating agent (polyimide PI nanopowder, particle size 80nm), 0.4 parts of hindered phenolic antioxidant (Irganox 1010), 0.9 parts of perfluoroalkyl ether crystallization regulator, and injects 3% of supercritical nitrogen gas as a foaming agent at a pressure of 28MPa and a temperature of 365℃.

[0057] The composite insulation layer 2 also includes an ultra-thin dense surface layer 22 that is coated on the polytetrafluoroethylene layer 21 by a co-extrusion process. The ultra-thin dense surface layer 22 is made of low-loss cross-linked polyethylene and has a thickness of 0.18 mm.

[0058] The outer radiating conductor 3 is a longitudinally welded annular corrugated copper tube. The surface of the outer radiating conductor 3 has a periodically arranged array of rectangular slots with unequal spacing along the axial direction. The long side of each rectangular slot forms a 12° angle with the cable axis. Adjacent rows of rectangular slots are staggered axially. The width of each rectangular slot is 0.6 mm, and its length is 5 mm. The ends of each rectangular slot have semi-circular chamfers with a radius of 0.4 mm. The staggered spacing between adjacent rows of slots is 2.0 mm, and the period length increases exponentially from 10 mm at the beginning to 30 mm at the end.

[0059] The rectangular slot is formed by femtosecond laser cutting, with a burr height of less than 5μm.

[0060] The formulation of the microwave absorbing layer 4, by weight, includes: 100 parts of polymer substrate (polypropylene PP), 55 parts of carbonyl iron powder (CIP, particle size 5μm, flake form, ball-milled for 7 hours), and hexagonal ferrite (BaFe). 12 O 19 28 parts of carbon nanotubes (CNTs) with a particle size of 2 μm, 4 parts of titanium ester coupling agent, and 4 parts of dispersant (polyethylene wax).

[0061] The thickness of the absorbing layer 4 is 0.4 mm.

[0062] The composite sheath layer 5 includes a flame-retardant polyolefin inner layer 51 (1.0 mm thick) and an ultraviolet-resistant, low-friction outer sheath layer 52 (0.5 mm thick) extruded onto the outside.

[0063] A method for manufacturing a high-frequency compatible, low-loss, leaky coaxial cable includes the following steps: S1: The copper strip is rolled into a round tube, the longitudinal seam is welded, and the diameter is expanded by rotation to form a hollow corrugated copper tube structure, forming inner conductor 1 with an inner diameter of 6.5mm and an outer diameter of 8.5mm, and the inside is filled with dry nitrogen. S2: 100 parts of PTFE dispersion resin, 6 parts of nano-nucleating agent (polyimide PI nanopowder, particle size 80nm), 0.4 parts of hindered phenolic antioxidant (Irganox 1010), and 0.9 parts of perfluoroalkyl ether crystallization regulator are mixed and injected with supercritical nitrogen gas accounting for 3% of the total resin mass as a foaming agent (injection pressure 28MPa, temperature 365℃). The mixture is extruded onto the inner conductor 1 at 35MPa and 350℃ to form a polytetrafluoroethylene layer 21. Then, cross-linked polyethylene is co-extruded over the polytetrafluoroethylene layer 21 to form an ultra-thin and dense surface layer 22, and finally, a composite insulation layer 2 is obtained. S3: Copper strip is wrapped around composite insulation layer 2, longitudinally welded to form copper tube, and then annular embossing is performed; S4: Use femtosecond laser cutting technology to open a rectangular slot array on the outer conductor obtained in step S3, control the axial misalignment distance between adjacent rows of rectangular slots, the pulse width of femtosecond laser cutting is 400 femtoseconds, and the repetition frequency is 1MHz; S5: Composed of 100 parts of polymer matrix (polypropylene PP), 55 parts of carbonyl iron powder (CIP, particle size 5μm, flakes, ball-milled for 7 hours), and hexagonal ferrite (BaFe). 12 O 19 28 parts of carbon nanotubes (CNTs) with a particle size of 2μm, 4 parts of titanium ester coupling agent, 2.5 parts of dispersant (polyethylene wax) are mixed and calendered into a 0.4mm thick strip, which is then wrapped around the grooved outer radiating conductor 3 and finally a double-layer co-extruded composite sheath layer 5 is formed.

[0064] The high-frequency compatible low-loss leaky coaxial cable provided in this embodiment achieves an attenuation constant of <5dB / 100m@100GHz and a VSWR of <1.2 in a wide frequency band of 1GHz-100GHz, and effectively suppresses high-order mode interference, significantly improving the transmission distance and coverage quality of 6G high-frequency signals, making it suitable for complex environments such as indoors and tunnels.

[0065] The performance specifications of the high-frequency compatible low-loss leaky coaxial cable provided in this embodiment are as follows: At the 100GHz frequency point, the attenuation constant is 4dB / 100m; The voltage standing wave ratio (VSWR) is 1.16 in the 1-100 GHz range; The absorbing layer 4 has a reflection loss of 13dB at 70GHz.

[0066] Comparative Example 1 It adopts conventional PE foaming and traditional figure-eight groove holes.

[0067] The difference between this comparative example and Example 1 is that the polytetrafluoroethylene layer in this comparative example is made of conventional physically foamed PE (75% foaming degree), without a microwave absorbing layer, and the rectangular slots are ordinary figure-eight slots (fixed period 8mm).

[0068] The leaky coaxial cable in this comparison has an attenuation constant of 11.5 dB / 100 m at 100 GHz and a maximum VSWR of 1.45.

[0069] Comparative Example 2 The difference between this comparative example and Example 1 is that no perfluoroalkyl ether crystallization regulator was added to the polytetrafluoroethylene layer in this comparative example. As a result, the foaming was uneven, the cell diameter was >200 μm, the dielectric loss tangent increased to 0.0015, and the attenuation constant increased to 6.8 dB / 100 m.

[0070] Comparative Example 3 The difference between this comparative example and Example 1 is that this comparative example does not have an absorbing layer. The results show that in the frequency band above 60 GHz, the longitudinal propagation of surface waves along the outer conductor causes the VSWR to rise to 1.35.

[0071] Comparative Example 4 The difference between this comparative example and Example 1 is that the slot period length in this comparative example is fixed at 12 mm, rather than increasing exponentially. The results show that the radiation is weak in the low-frequency band (<10 GHz), and the VSWR rises to 1.30 in the frequency band above 80 GHz, indicating a decrease in high-frequency matching performance.

[0072] Table 1 shows a summary table of the performance of Examples 1-2 and Comparative Examples 1-4.

[0073] Table 1

[0074] As shown in Table 1, the present invention achieves excellent transmission performance over a wide bandwidth by using a high foaming PTFE formulation, an exponentially increasing periodic slot structure, and an absorbing layer to effectively suppress high-order mode interference and frequency band abrupt changes while maintaining low attenuation.

[0075] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0076] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A high-frequency compatible, low-loss, leaky coaxial cable, characterized in that, From the inside out, it includes an inner conductor, a composite insulation layer, a radiating outer conductor, a wave-absorbing layer, and a composite sheath layer. The inner conductor is a hollow corrugated copper tube structure, filled with a gas with a dielectric constant close to 1 or a cross-shaped support frame. The composite insulation layer comprises a polytetrafluoroethylene layer with a foaming degree of 85-92% and an ultra-thin dense surface layer covering the polytetrafluoroethylene layer, the polytetrafluoroethylene layer has a cell diameter less than 100 microns and a cell density greater than 10 9 / cm 3 , and the ultra-thin dense surface layer is made of low-loss cross-linked polyethylene and has a thickness of 0.1-0.2 mm. The outer radiating conductor is provided with a single rectangular slot structure with an exponentially increasing periodic length along the axial direction. The microwave absorbing layer comprises, by weight, 100 parts of polymer substrate, 40-60 parts of carbonyl iron powder, 20-30 parts of hexagonal ferrite, 1-5 parts of carbon nanotubes, 1-3 parts of coupling agent, and 2-5 parts of dispersant.

2. The high-frequency compatible low-loss leakage coaxial cable according to claim 1, characterized in that, The formulation of the polytetrafluoroethylene layer, by weight, includes: 100 parts of PTFE dispersion resin, 3-8 parts of nano-nucleating agent, 0.2-0.5 parts of hindered phenolic antioxidant, 0.5-1 parts of perfluoroalkyl ether crystallization regulator, and supercritical nitrogen gas accounting for 1.5-3.5% of the total resin mass as a foaming agent.

3. The high-frequency compatible low-loss leakage coaxial cable according to claim 1, characterized in that, The outer radiating conductor is provided with an array of rectangular slots arranged periodically along the axial direction. The long side of the rectangular slots makes an angle of 10°-20° with the cable axis. Adjacent rows of rectangular slots are staggered in the axial direction, with a staggering distance of 1 / 4-1 / 2 of the length of the rectangular slot. The two ends of the rectangular slots are provided with semi-circular chamfers with a radius of 0.2-0.5mm.

4. The high-frequency compatible low-loss leakage coaxial cable according to claim 3, characterized in that, The periodic length of the rectangular slot increases exponentially along the axial direction, and the width of the rectangular slot is 0.3-1.2 mm and the length is 2-8 mm.

5. The high-frequency compatible low-loss leakage coaxial cable according to claim 1, characterized in that, The thickness of the absorbing layer is 0.2-0.5 mm.

6. The high-frequency compatible low-loss leakage coaxial cable according to claim 1, characterized in that, The outer radiating conductor is a longitudinally welded annular corrugated copper tube; the composite sheath layer includes a flame-retardant polyolefin inner layer and an ultraviolet-resistant, low-friction sheath outer layer extruded onto the outside.

7. A method for preparing a high-frequency compatible low-loss leakage coaxial cable according to any one of claims 1-6, characterized in that, Includes the following steps: S1: The copper strip is rolled into a round tube, the longitudinal seam is welded, and the diameter is expanded by rotation to form a hollow corrugated copper tube structure, forming an inner conductor, which is filled with gas or a support skeleton with a dielectric constant close to 1. S2: Mix 100 parts of PTFE dispersion resin, 3-8 parts of nano nucleating agent, 0.2-0.5 parts of hindered phenolic antioxidant and 0.5-1 parts of perfluoroalkyl ether crystallization regulator evenly, and inject 1.5-3.5% of supercritical nitrogen gas as a foaming agent. Extrude the mixture onto the inner conductor at 20-35 MPa and 350-380℃ to form a microporous polytetrafluoroethylene layer. Then, co-extrude cross-linked polyethylene onto the outside of the microporous polytetrafluoroethylene layer to form an ultra-thin and dense surface layer, and finally obtain a composite insulation layer. S3: Copper strip is wrapped on the composite insulation layer, longitudinally welded to form a copper tube, and then annular corrugation is performed; S4: Use femtosecond laser cutting technology to open a rectangular slot array on the outer conductor obtained in step S3, control the axial misalignment distance between two adjacent rows of rectangular slots, the pulse width of femtosecond laser cutting is less than 500 femtoseconds, and the repetition frequency is 100kHz-1MHz; S5: The microwave absorbing band is prepared by using 100 parts of polymer substrate, 40-60 parts of carbonyl iron powder, 20-30 parts of hexagonal ferrite, 1-5 parts of carbon nanotubes, 1-3 parts of coupling agent and 2-5 parts of dispersant. It is then longitudinally wrapped or wrapped around the grooved outer radiation conductor, and finally a double-layer co-extruded composite sheath layer is formed.

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